A fuel cell vehicle receives power from two power supplying sources, namely a fuel cell stack and a high voltage battery, to operate a motor or to recover regenerative brake energy, and the fuel cell vehicle includes a stack main relay and a battery relay for connecting or blocking power provided from each power supplying source.
When a driver drives the fuel cell vehicle in a hybrid mode, the fuel cell vehicle runs while the stack main relay and the battery relay are in closed state.
However, when the driver stops driving the fuel cell vehicle, a remaining voltage of a fuel cell stack has to be completely consumed while shutting down the operation thereof. For this, the remaining voltage is forcibly consumed by opening the stack main relay while an air supply to the fuel cell is stopped, the fuel cell stack is connected to a resistor by using a resistor relay, and thus forcibly reacting remaining hydrogen gas and oxygen gas within the fuel cell stack.
Then, when the stack voltage has been consumed to some extent, an operation of a coolant pump (CSP) is stopped, an operation of a low Voltage DC/DC converter (LDC) is stopped, and then the battery relay is opened.
Herein, in order to consume the stack voltage, two relays are used for the resistor relay. The resistor relays are used for blocking a voltage being raised which is generated by reaction between atmospheric air therein and remaining hydrogen gas when the vehicle enters a power-OFF state after consuming the stack voltage, and for consuming a remaining voltage of the fuel cell stack when an emergency situation such as a collision occurs so that the controller cannot normally operate, or when one resistor relay is damaged so that normal consuming of the stack voltage is performed by automatically closing other resistor relays.
In an emergency situation such as a collision, it is a legal requirement to drop the stack voltage to less than a certain voltage level within a certain time.
However, the method of shutting down operation of the fuel cell system described as above has the following problems.
When shutting down the vehicle operation, there is high probability that the stack voltage is maintained at a high level, a high voltage DC/DC converter (HDC) keeps controlling the voltage, and the coolant pump (CSP) and the LDC are in operation.
Herein, as voltages at front and rear ends of the stack main relay are identical, and the stack main relay is in a closed state, although its value is not large, current is still generated in the stack. When the stack main relay is opened at the above situation, fusion damage of the stack main relay may be generated.
In addition, after opening the stack main relay, the resistor relay is closed for consuming the stack voltage. Herein, since a hydrogen gas supply to the stack is maintained, new hydrogen gas is continuously supplied to the stack as much as the lost hydrogen gas in response to the consumption of the voltage.
Accordingly, energy used for consuming the remaining voltage of the stack is generated to heat by the resistor, thus unnecessary hydrogen gas consumption occurs. In addition, when current is generated while hydrogen gas is insufficient within the stack, stack damage may cause.
In addition, the stack voltage is consumed to some extent by closing one resistor relay, and the closed relay is opened and then the other resistor relay is closed, at the above crossing timing, while current is still generated in the stack, thereby causing intermittent resistance relay damage.
In addition, when instantaneous inrush current that may be generated at the above crossing timing between the two relays is repeatedly occurs, fusion damage of the resistor relay may be generated by the accumulated damage.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.